Liquid crystal display devices which exploit the light scattering and transmitting properties of discrete quantities of liquid crystal can be fabricated by polymerization induced phase separation of homogeneous solutions of liquid crystal and various synthetic polymers. The liquid crystal-polymeric material can be formed as a film or sheet and positioned between transparent conducting electrodes to form an electrically switchable light shutter.
Liquid crystals useful for light scattering displays have two indices of refraction: an extraordinary index of refraction n.sub.e measured along the long axis of the liquid crystals, and a smaller ordinary index of refraction n.sub.o, measured in a plane perpendicular to the long axis. The long axis of the liquid crystal defines its optic axis.
In polymer dispersed liquid crystal (PDLC) devices, phase separated liquid crystal microdroplets are dispersed in a polymeric matrix having an index of refraction n.sub.p. Such PDLC devices will either scatter or transmit incident light depending upon the relationship among the indices of refraction and dependent upon the microdroplets being of a size to scatter incident light, e.g., on the order of 0.1 to 10- microns.
In the absence of an applied field, the optic axes of the microdroplets have no preferred direction in which to point in the plane, so that incident light encounters a mismatch between the refraction index n.sub.p of the matrix and the average refraction index (.about.n.sub.e) of the microdroplets. The result of the mismatch is that the light is scattered and the device appears opaque. Application of an electric field across the sheet of liquid crystalline-polymeric material causes the optic axes to align parallel to the field and normal to the surface of the sheet. Incident light detects no mismatch between average refractive index of liquid crystal droplet (.about.n.sub.o) and n.sub.p and is transmitted so that the device appears clear.